Steps:

1. Measure the height from the top of the existing fireplace to the ceiling. This will be the measurement used for the height of the MDF. 2. Measure the width of the existing fireplace. 3. Using the T-square, transfer the dimensions onto the MDF. 4. To create the crown and arch of the top of the mantel, you will need to decide how far to extend the width and then mark the MDF. This measurement needs to be equal on both sides. 5. Decide the height of the crown and mark it on the MDF. 6. Place a large plate or bowl upside down and use its arc to connect the bottom of the crown to the inset of the mantel. 7. Use the jigsaw to cut out the frame drawn on the MDF. 8. Any accent pieces can be cut out from the scraps of MDF and nailed to the face of the mantel if desired. For the pictured project, four symmetrical stripes were cut out and attached with the wood glue and the nail gun. We then cut out a diamond and centered it in the middle of the mantel. 9. Using a router, finish off the outside edges of the frame. Be sure to leave the top and bottom unfinished. This will help to create a seamless transition between the old fireplace and the new mantel. If desired, the accent pieces that have been attached can also be routed. 10. Rest the entire frame on the existing fireplace. 11. Run a bead of caulk across the top and bottom of the frame. This will seal it into place. 12. Paint both the new frame and the fireplace.